Time-, Energy-, and Phase-Resolved Second-Harmonic Generation at Semiconductor Interfaces

Nelson, Cory A.; Luo, Jingdong; Jen, Alex K.‐Y.; Laghumavarapu, Ramesh B.; Huffaker, Diana L.; Zhu, Xiaoyang

doi:10.1021/jp5094614

Cited by 20 publications

(23 citation statements)

References 46 publications

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“…Regarding the experimental results, the linker system apparently adds an equal unknown background contribution to the SHG signal intensities measured for both PSSs and therefore reduces the apparent NLO contrast. Furthermore, as the phase information 46 is not accessed in our experiment, a negative interference between the chromophore and background contributions cannot be excluded. However, due to the low film thickness we expect only a small phase shift, which does not lead to destructive interference.…”

Section: Calculated Molecular Geometries and Hyperpolarizabilities Pmentioning

confidence: 95%

Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers

Schulze

Utecht

Moldt

et al. 2015

Phys. Chem. Chem. Phys.

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The combination of photochromic and nonlinear optical (NLO) properties of azobenzene-functionalized self-assembled monolayers (SAMs) constitutes an intriguing step towards novel photonic and optoelectronic devices. By utilizing the second-order NLO process of second harmonic generation (SHG), supported by density-functional theory and correlated wave function method calculations, we demonstrate that the photochromic interface provides the necessary prerequisites en route towards possible future technical applications: we find a high NLO contrast on the order of 16% between the switching states. These are furthermore accessible reversibly and with high efficiencies in terms of cross sections on the order of 10(-18) cm(2) for both photoisomerization reactions, i.e., drivable by means of low-power LED light sources. Finally, both photostationary states (PSSs) are thermally stable at ambient conditions.

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Section: Calculated Molecular Geometries and Hyperpolarizabilities Pmentioning

confidence: 95%

Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers

Schulze

Utecht

Moldt

et al. 2015

Phys. Chem. Chem. Phys.

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“…Recent studies showed that charge transfer occurs at semiconductor/organic thin film interfaces with timeresolved electric-field induced second harmonic generation (SHG), with the loss of spectral information. [13][14][15][16] Early efforts have also demonstrated the ultrafast relaxation of the surface photo-voltage (SPV) effect on semiconductors by timeresolved photoemission spectroscopy. [17][18][19] The time evolution of the electric field was demonstrated in the surface layer of semiconductors by measuring the kinetic-energy shifts of photoelectrons.…”

Section: Introductionmentioning

confidence: 99%

Development of ultrafast broadband electronic sum frequency generation for charge dynamics at surfaces and interfaces

Deng

Qian

Rao

2019

The Journal of Chemical Physics

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Understandings of population and relaxation of charges at surfaces and interfaces are essential to improve charge collection efficiency for energy conversion, catalysis, and photosynthesis. Existing time-resolved surface and interface tools are limited to either under ultrahigh vacuum or in a narrow wavelength region with the loss of spectral information. There lacks an efficient time-resolved surface/interface-specific electronic spectroscopy under ambient conditions for the ultrafast surface/interface dynamics. Here we developed a novel technique for surface/interface-specific broadband electronic sum frequency generation (ESFG). The broadband ESFG was based on a stable two-stage BiB 3 O 6 crystal-based optical parametric amplifier, which generates a strong broadband shortwave infrared (SWIR) from 1200 nm to 2400 nm. A resultant surface spectrum covers almost all visible light from 480 nm to 760 nm, combined a broadband electronic second harmonic generation (ESHG) with the ESFG from the SWIR laser source. We further developed the steady-state and transient broadband ESFG and ESHG techniques to investigate the structure and dynamics of charges at oxidized p-type GaAs (100) semiconductor surfaces, as an example. Both the steady-state and transient experiments have shown that two surface states exist inside the bandgap of the GaAs. The kinetic processes at the GaAs surface include both the population and recombination of the surface states after photoexcitation, in addition to the build-up of the space photo-voltage (SPV). The build-up SPV occurs with a rate of 0.56 ± 0.07 ps −1 , while the population rate of the surface states exhibits a two-body behavior with a rate constant of (0.012 ± 0.002) × 10 12 s −1 cm 2. The photo-generated electron-hole pairs near the surface recombine with a rate of 0.002 ± 0.0002 ps −1 for the oxidized p-type GaAs (100). All the methodologies developed here are readily applied to any optically accessible interfaces and surfaces, in particular buried interfaces under ambient conditions.

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“…An experimental aspect, second harmonic generation (SHG), has been used to study photoinduced charge separation dynamics in organic semiconductor thin films using the time-resolved spectra technique. Some meaningful results have been obtained, including charge separation from a gradient in excitation density and differential electron/hole mobility in model systems of fullerene (C70) and semiconductor interfaces 28 29 . However, it is reasonable to believe that using quadratic response theory will not considerably affect our qualitative results for photoinduced charge transport efficiency controlled by external electric field.…”

Section: Resultsmentioning

confidence: 99%

Photoinduced Charge Transport in a BHJ Solar Cell Controlled by an External Electric Field

Feng

Sun

2015

Sci Rep

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This study investigated theoretical photoinduced charge transport in a bulk heterojunction (BHJ) solar cell controlled by an external electric field. Our method for visualizing charge difference density identified the excited state properties of photoinduced charge transfer, and the charge transfer excited states were distinguished from local excited states during electronic transitions. Furthermore, the calculated rates for the charge transfer revealed that the charge transfer was strongly influenced by the external electric field. The external electric field accelerated the rate of charge transfer by up to one order when charge recombination was significantly restrained. Our research demonstrated that photoinduced charge transport controlled by an external electric field in a BHJ solar cell is efficient, and the exciton dissociation is not the limiting factor in organic solar cells.Our research should aid in the rational design of a novel conjugated system of organic solar cells.

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Time-, Energy-, and Phase-Resolved Second-Harmonic Generation at Semiconductor Interfaces

Cited by 20 publications

References 46 publications

Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers

Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers

Development of ultrafast broadband electronic sum frequency generation for charge dynamics at surfaces and interfaces

Photoinduced Charge Transport in a BHJ Solar Cell Controlled by an External Electric Field

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